1. Field of the Invention
The present invention relates generally to silicon wafer handling machines, and more particularly is a pod loader interface that is adapted to unload and reload SMIF (Standard Mechanical InterFace) pods.
2. Description of the Prior Art
Handling of silicon wafers is critical to the integrated circuit (IC) manufacturing process. Any physical damage to the wafers will, of course, decrease the chip yield, which is a prime consideration in the profitability of semiconductor manufacturing. Contamination of the wafer by particulate or other contaminants also decrease chip yield. For several decades the semiconductor manufacturing industry has addressed its need to reduce contamination during manufacturing by replacing human operators, as much as practicable, with robot wafer handling equipment.
The desire to shield wafers from contaminants has led the semiconductor industry to the development and use of SMIF pods. SMIF pods allow wafers to be transported in a clean, sealed environment, so they are not exposed to ambient air.
Once the SMIF pods reach their destination, they must be opened, and the wafer carrier inside must be placed in position for the desired process operation. If the unloading and positioning operation is performed manually, the wafers are subjected to the usual risk of damage from mishandling as well as increased exposure to contamination.
Pod loader interfaces are used extensively in the semiconductor industry to automatically unload a SMIF pod and position the wafers held in a wafer carrier for the next process operation, and then reload the wafers and the wafer carrier when the process step is completed. In general, these pod loader interfaces include an arm for transporting the wafer carrier and wafers between a clean mini-environment established within the pod loader interface and the processing tool which performs the process step. The arm of the pod loader interface includes an end effector that grasps and secures the wafer carrier.
One difficulty experienced in integrating a pod loader interface with a semiconductor processing tool is mechanically aligning the interface and the tool so the end effector may reliably grasp and secure a wafer carrier present within the processing tool and/or pod loader interface. It is also advantageous if a pod loader interface can be readily adapted to deliver wafer carriers to semiconductor processing tools in any arbitrarily chosen orientation.
Accordingly, it is an object of the present invention to provide a means to more reliably automatically open and unload, and subsequently reload and close, a SMIF pod.
Another object of the present invention is to provide an end effector for an arm of a pod loader interface that relaxes alignment tolerances between the pod loader interface and the semiconductor processing tool.
Yet another object of the present invention is to provide an end effector for an arm included in a pod loader interface that readily accommodates varying positions for wafer carriers in semiconductor processing tools.
Briefly, the present invention in one aspect is an end effector for a pod loader interface that automatically opens a SMIF pod and unloads the contents thereof. The pod loader interface includes an elevator that raises a SMIF pod cover away from a SMIF pod base to reveal the wafer carrier contained within the sealed SMIF pod. An articulated arm of the pod loader interface thereafter reaches through an opening in a bulkhead thereof, secures the wafer carrier and withdraws it through the bulkhead opening. The wafer carrier is then placed at a location within the processing tool where it can be operated upon by the processing tool to perform a step in the manufacturing process. The pod loader interface includes an integrated clean air system to maintain the wafers in a clean environment.
A specific aspect if the present invention is an end effector, attached to the articulated arm of the pod loader interface, that grips the wafer carrier. This end effector includes a gripper plate that attaches to the articulated arm. Aligning means secured to the gripper plate properly align the end effector with the wafer carrier. A pair of gripper blades are separated from each other along and are coupled to the gripper plate. During gripping of the wafer carrier by this end effector, the gripper blades initially close toward each other and then draw nearer to the gripper plate. The end effector also includes drive means, that is secured to the gripper plate, which energize movement of the gripper blades for gripping the wafer carrier. By drawing the gripper blades nearer to the gripper plate, this end effector accommodates greater variations among wafer carrier positions both within the pod loader interface and within the processing tool.
Another aspect of the present invention is an end effector which also includes an outer and an inner nested pair of U-shaped yokes which attach the gripper plate to the articulated arm. Each of the U-shaped yokes has a base from opposite ends of which extend two parallel sides. The base of the outer U-shaped yoke attaches directly to the articulated arm. To permit relative rotation of the U-shaped yokes with respect to each other, the outer and inner U-shaped yokes are joined by rotational joints located at ends of each of the sides furthest from their bases. The gripper plate, preferably that described in the preceding paragraph, is fastened to the base of the inner U-shaped yoke between the sides thereof. This end effector also includes a carrier rotary-drive that is coupled between the U-shaped yokes to energizes rotation of the outer and inner U-shaped yokes with respect to each other. In this way, the end effector may rotate a wafer carrier that is gripped by the gripper blades about an axis that:
1. passes through the rotational joints between ends of the sides of the U-shaped yokes; and
2. is oriented parallel to semiconductor wafers held in the wafer carrier.
Yet another aspect of the present invention is an improved mechanical rotary drive for a forearm of the articulated arm. In this improved rotary drive, a notched belt, formed into a continuous loop and tensed by a differential screw that joins ends of the belt, couples together pulleys that are located at the shoulder and elbow joints of the articulated arm. Respective diameters of the pulleys and lengths of the upper arm and forearm are arranged so rotation of the upper arm about the shoulder joint effects substantially straight line motion of the wrist joint during transportation of the wafer carrier.
Yet another aspect of the present invention is an end effector rotary-drive included in a forearm of the articulated arm. The end effector rotary-drive is coupled through a wrist joint of the forearm to the gripper plate of the end effector. In this way, the end effector rotary-drive can independently rotate the gripper plate with respect to the forearm about an axis that is oriented perpendicular to a plane in which the wrist joint moves when the articulated arm transports semiconductor wafers held in the wafer carrier to or from the processing tool.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.